This invention relates to printing devices, and more particularly to printwheels for impact printers.
Printwheels for use with impact printers have been available for many years. Sometimes referred to as a "daisy wheel", the printwheel is a disk-shaped element, having a annular disk central region surrounded by radially extending character arms. At its tip, each character arm includes a character "slug" having a print face bearing a raised reversed facsimile of a member of a host language character set. The sequence of character slugs about the printwheel circumference is generally determined by industry standard.
Within the impact printer, the printwheel typically is attached to a rotatable printwheel spindle. The end portion of a single character arm and the corresponding character slug are positioned between a striking element and an opposed platen with the print face being opposite the platen. A transfer medium (such as an inked ribbon) and a print medium (such as paper) are positioned between the print face of the printwheel and the platen. In operation, the printwheel spindle rotates, so that the character slugs successively pass before the striking element. Synchronously with the movement of the printwheel, the striking element, e.g., a hammer, is selectively activated when a desired character slug is before it, to strike the character arm, causing deflection of the character arm so that the print face drives the inked ribbon against the print medium and platen. The striking element then retracts and the character arm returns to its normal position. As a result of this operation, ink is transferred from the ribbon to the print medium, thereby forming the character image of the driven slug on the medium.
Conventional printwheels are often formed using metal coated phenolic structures. When such printwheels are used in conjunction with printers coupled to computers and word processors, the printwheels are typically subjected to repeated, high-speed striking. This use causes the printwheel character arms to become less resilient with use, resulting in degradation of performance. The repeated impacting of the character slugs additionally results in surface wear on the character slug print face causing loss of print character crispness. Consequently, conventional printwheels must be replaced at a relatively high frequency in order to maintain acceptable printing performance.
The object of this invention is to provide an improved printwheel with long lasting character slug sharpness and character arm resiliance.
A further object of the invention is also to provide a lightweight print wheel with improved vibration damping characteristics.